Projection capacitive touch screen is a sensor film sealing the conductive fine-wires, which has advantages of precise sensing positioning, flexibility and high transparency. It could be used for precise touch positioning of 12-inch touch screens, as well as precise interactive projection.
Projected capacitive technology is a touch control technology of manufacturing horizontal and vertical electrode matrixes on a glass or transparent film surface and detecting finger touch through the capacitance changes of those electrodes. This technique involves two types according to the different ways in that the capacitance is produced.
The first type is self-capacitance touch screen. Horizontal and longitudinal electrode arrays of transparent conductive material are arranged on the surface of glass or transparent film. Those horizontal and longitudinal electrodes form a capacitance with ground respectively, which is commonly referred to as the self-capacitance, that is, the electrode to ground capacitance. When the finger touches the capacitive touch screen, the capacitance of the finger will be superimposed on the screen capacitor, so that the screen capacity increases. In the touch detection, the self-capacitance touch screen is in turn detected in the horizontal and vertical electrode array respectively. According to the changes of the capacitance before and after touch, horizontal coordinates and longitudinal coordinates could be determined respectively, which then are combined into a plane touch coordinates. The scanning manner of the self-capacitance touch screen is corresponding to project the touch point to the X axis and Y axis direction, then calculate the coordinates in the X axis and Y axis, direction to, and finally combine them into the touch point coordinates.
The second type is mutual capacitance touch screen. Horizontal and longitudinal electrode arrays of transparent conductive material are arranged on the surface of glass or transparent film. It differs from the self-capacitance touch screen in that the capacitance would be formed in the intersection of two sets of electrodes, that is, the two sets of electrodes constitute the two poles of capacitance respectively. When the finger touches the capacitive touch screen, it affects the coupling between the two electrodes near the touch point, thereby changing the capacitance between the two electrodes. When the mutual capacitance is detected, the horizontal electrodes sequentially emit excitation signals, and all the electrodes in the longitudinal direction receive signals at the same time, so that the capacitance value of the intersection of all the horizontal and vertical electrodes can be obtained, that is, the capacitance of the two-dimensional plane of the whole touch screen. According to the touch screen two-dimensional capacitance change data, the coordinates of each touch point could be calculated. Therefore, even if there are multiple touch points on the screen, the real coordinates of each touch point can be calculated.
The current large-size touch screen (12-inch or more) market is mainly occupied by the infrared screen. Infrared screen works by utilizing the infrared rays emitted around it. As long as there is an object to cut off the infrared, the screen will be able to respond. Capacitive touch screen is technically superior to the infrared screen in viewing of the following aspects:
1. Infrared screen will have action as long as anything blocks infrared, which would easily lead to false operation. For example, in winter if some objects such as clothes touch the infrared screen, it would produce a false operation.
2. Infrared screen is not easy to waterproof.
3. Infrared screen in the light irradiation is prone to drift or even has no action; therefore infrared screen is not suitable for outdoor use.
4. Capacitive touch screen has higher resolution, so the accuracy of products is much higher.
At present, there are two main methods for producing large-sized capacitive touch film.
One production method is the use of conductive oil film jet heating sintered into conductive electrodes. However, in the actual production, conductive oil film is difficult to control the diameter of the printed line, and it is easy to splash to the non-printing area to form impurity points. Print speed is relatively slow.
The other one is producing conductive electrodes by the use of 3D printing and heating sintering. However, in the actual production, printing speed is relatively slow, and the process is more complex and has low yield rate.
Therefore, the current large-size capacitive touch film problems lie in complex production process, slow production, low yield and high cost.